Process for manufacturing thermoplastic compositions and containers made of such compositions

ABSTRACT

A process for manufacturing thermoplastic materials having an elevated gas impermeability and/or improved physical properties. This process is characterized in that it comprises mixing at least partially incompatible polymers, gelling them by the combined action of heat, pressure and kneading. The gelled mixture is then subjected to laminar flow through substantially parallel surfaces in which the ratio of the length of the surfaces to the distance between them is greater than 10. 
     A thermoplastic material having increased gas impermeability as well as containers made out of said materials. 
     A packaging method in which the thermoplastic materials of the invention are used to package oxygen sensitive materials.

This is a division, of application Ser. No. 844,310, filed Oct. 21,1977, pending in group (160).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process for manufacturing compositions ofthermoplastic materials having an elevated gas impermeability and/orcertain improved physical and mechanical properties which can be usedfor example in the field of packaging carbonated liquids.

2. Description of the Prior Art

Certain uses of plastic materials require a very high gasimpermeability. It is also known that this impermeability is selectiveand that it varies unpredictably. The gas permeability coefficients of agiven plastic material may differ enormously depending on the particulargas. It should likewise be noted that these differences can becomplemented, for example a plastic material can be permeable to gas Aand impermeable to gas B whereas the complementary material could beimpermeable to gas A and permeable to gas B Thus it sems normal tocombine these two materials in order to obtain a composition having ahigh impermeability coefficient with respect to both gases A and B.

It often occurs that the materials which one wants to combine areimcompatible. This results, for example, in the coextrusion ofmultilayered complexes, in a product which tends to peel apartquasi-spontaneously and is thus not suited for applications requiring aminimum amount of cohesion and adherence.

This manifests itself further when, for example, a mixture ofincompatible polymers are extruded, in the manufacture of a producthaving a non-homogeneous structure of composition. This heterogenity canbe seen with the naked eye or with a magnifying glass or occasionallywith the aid of a high-power microscope. The product obtained thus has astructure which resembles that of an emulsion or of a solidifiedsuspension having a continuous as well as a discontinuous phase. If thepermeability of this product is measured, it is found that it isapproximately that of the continuous phase. The benefit of the reductionin permeability which the polymer in the discontinuous phase would havebeen able to add, which would have been desirable for certainapplications, is not achieved.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a process of manufacturingcompositions of thermoplastic materials having an increased gasimpermeability which process can be performed in a simple and economicalmanner on early available current material.

In the process according to the invention, the polymers which are atleast partially incompatable are mixed by any conventional or knownmeans. The mixture is then gelled by the combined action of heat,pressure and kneading. The gelled mixture is then caused to flowlaminarly between substantially parallel surfaces such as flat platedies, annular dies or dies of any cross-sectional shape. The ratio ofthe lengths of these surfaces in the direction of the flow of thematerial and the distance between these surfaces being greater thanabout 10 and preferably greater than about 20. A mixture of polymers isthus obtained whose structure comprises a continuous phase and adiscontinuous phase each containing a polymer or a mixture of polymerswhich are themselves compatible. The discontinuous phase has a generallylamellar form of low thickness in proportion to its length and width andis distributed throughout the continuous phase parallel to the majordimensions of the films, sheets, plates or parisons having a circular orany other cross-section when leaving the die.

According to one characteristic of the invention, the continuous phaseincludes polyvinyl chloride and the discontinuous phase includes apolyvinyl type alcohol or a copolymer which is composed primarily of avinyl alcohol, the proportions of the mixture being 100 parts by weightof polyvinyl chloride per about 1 to 100, preferably about 5 to about 30parts, by weight of polyvinyl alcohol. The value of K of the polyvinylchloride is between about 50 and about 80, preferably between about 56and 62. The extend of hydrolysis of the polyvinyl alcohol being betweenabout 50 and 100%, preferably between about 80 and about 95%. Theviscosity at 20° C. of a 4% aqueous solution of the polyvinyl alcoholsolution being between about 2 and about 70 cP, preferably between 4 and10 cP.

Naturally the mixture may also contain any conventional additives suchas stabilizers, lubricants, coloring agents, agents which add shockresistance, etc., which may be added and are normally added during themanufacture of rigid polyvinyl chloride compounds.

One of the advantages of the process of the invention is the fact thatit does not require a number of extruders or dies equal to the number ofused polymers and binders.

Furthermore, it does not require successive operations by differentmachines such as the processes of coextrusion, overlaying, coating,pressing of the two layers, layer extrusion and other known processes ofmanufacturing products made out of plastic materials having amultilayered structure.

As used in this specification, the terms "polymer" and "plasticmaterials" are used to denote all natural or artificial macromolecularthermoplastic materials or such mterials which are obtainedsynthetically by polymerization, polycondensation or other chemicalreactions whether they contain or not any of the diverse additivesnormally added for reasons of modification, use or economy.

In terms of the process, the term "incompatibility" as used throughoutthe specification is defined such that a polymer is considered to bepartially or totally incompatible with another polymer if mixture of thetwo polymers in certain proportions and under certain mixing conditionsresults in plastic materials having a non-homogeneous structure orcomposition.

The phase "a mixture of polymers" is taken to mean a powdered, granularor solid mass containing two or more polymers after they were subjectedto homogenizing processes, as particles or macromolecules, in machinesnormally used for these operations by the plastics industry such as:slow or fast mixers, internal or cylindrical kneaders,granulator-extruders, granulators, etc.

The process of the invention contemplates, preferably, the use of singlescrew, double screw, or multiple screw extruders having a planetaryscrew and/or a plate for the transformation of the mixtures intofinished or semifinished products. Nevertheless, any other machinecapable of bringing the mixture into the melted state and making it flowcontinuously or intermittantly through a die or between close parallelsurfaces may be used.

The laminar flow necessary for the formation of the lamellar structureis obtained by the passage of the melted material through one or severaldies. The outlet of the die may be circular, linear or of any otherprofile or shape depending on the geometrical shape of the product whichone wants to manufacture such as for example: hollow bodies having across-section which is cylindrical, oval or square, films and smooth ortextured surfaces, etc. A significant consideration is the length, inthe direction of flow, of the constant cross-sectional orifice segmentof the die, also known as "die land", on which the creation of lamellarlayers depends. The optimal length is a function of the rheoloicalproperties of the material being treated, the nature of the surface ofthe die, the flow rate of the material as well as other parameters whichwill be readily apparent and which are necessary to achieve the desiredflow scheme.

A further aim of the inventio is to provide an improved thermoplasticmaterial which comprises at least two polymers which are at leastpartially incompatible polymers. The material has a continuous and adiscontinuous phase which each include a polymer or mixture ofcompatible polymers. The discontinuous phase is in the form of lamellarlayers which are relatively thin with respect to their length and widthand are distributed in the continuous phase parallel to the majordimensions of the thermoplastic material.

In a particular embodiment of the invention the continuous phaseincludes polyvinyl chloride and the discontinuous phase includes apolyvinyl alcohol or a copolymer composed primarily of polyvinylalcohol, the ratio of PVC to polyvinyl alcohol being between about 100:1and about 1:1.

In a preferred embodiment of the invention, the K value of the polyvinylchloride is between about 50 and about 80, the extent of hydrolysis ofthe polyvinyl alcohol is between about 50 and 100% and the viscosity ofthe polyvinyl alcohol used in a 4% aqueous solution is between about 2and about 70 cP.

A further aim of the invention is the fabrication of a container madeout of the material discussed above which may be used for edibles aswell as non-edibles.

The invention has furthermore as an object a container made out of thematerial described above which contains a carbonated liquid.

Finally, an object of the invention is to provide a method of protectingan oxygen sensitive material by packaging it in a container made out ofthe material of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates by way of exemple a microphotograph magnified 50times of a section of the wall of an extruded flask when using thecomposition of the invention which has been treated in boiling water inorder to make the lamellar structure visible.

The following examples, set forth merely for purposes of illustration,demonstrate the performance and applications of the process.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1

Mixtures 1, 2 and 3 are prepared as follows:

    ______________________________________                                                        Mixture                                                                       No 1   No 2     No 3                                          COMPONENTS        (parts by weight)                                           ______________________________________                                        PVC suspension, homopolymer                                                                     100      100      100                                       having a value of K = 57                                                      PVAL.sup.(1)      0        20       30                                        PARALOID® K 120 N                                                                           1        1        1                                         thio-tin stabiizer                                                                              0.3      0.3      0.3                                       (solid)                                                                       CIRE OP® lubricant                                                                          0.3      0.3      0.3                                       ______________________________________                                        .sup.(1) Poly-(vinyl alcohol) having the following characteristics:           Viscosity in a 4% aqueous                                                     solution               5 cP                                                   Extent of hydrolysis   88 mole %                                              Degree of polymerization                                                                             550                                                    ______________________________________                                    

The PVAL is dried under vacuum before being used.

The mixing takes place in a rapid Papenmeier mixer until the temperaturereaches 90° C.

One part of each of the mixtues is kneaded in a mixer having cylindersheated to a temperature of 180° C. for 5 minutes at the end of which,sheets, having a thickness of 0.5 mm, are drawn out.

The sheets are pressed to form plates having a thickness of 0.1 mm forthe measurement of permeability to O₂ and CO₂.

The pressing of the plates is effected by a 100 mm compression typepress made by LESCUYER and VILLENEUVE. The conditions during compressionare as follows:

-Temperature of the plates: 180° C.

-Preheated for two minutes

-Pressing for 4 minutes at 200 bars pressure.

It is observed, and the results of the measurements given below confirm,that the technique of drawing and pressing the plates does not in and ofitself result in a composition having a lamellar structure.

Another portion of the mixture is transformed into 250 cc flasks byblower extrusion with a HESTA model B33 S11 machine, equipped with asimple straight head and a circular die tube with a gap or clearance atthe outlet of 1.5 mm and a die-land of 45 mm which thus corresponds to aratio such as was defined hereinabove of 30/1.

The conditions of blower extrusion are:

-temperature profile from the inlet to the outlet165°-160°-165°-155°-200° C.

-screw speed: 60 rpm

-air blower pressure: 3 bars

-cycle: 11 seconds

The walls of the flask having a thickness of approximately 0.65 mmobtained from mixtures 2 and 3 (but not those obtained from mixture 1)have a lamellar structure visible under the microscope when cut withscissors or by crushing the flasks by hand.

Plates of 0.1 mm are made from the walls of the flasks in the samemanner as those made from the sheets of the cylinder mixer.

Measurement of the permeability to O₂ and CO₂ at 22° C. are made in thefollowing manner.

The measurement cell is divided into two compartments by the plate whosepermeability is to be measured. The testing gas is present in one of thecompartments at a pressure of 4 bars while the other compartment isswept with pure nitrogen. The gas going through the plate is entrainedby the nitrogen and measured.

The measurement is carried out as follows:

With respect to the oxygen, a HERSCH battery is used in which thelead-platinum electrodes are separated by a porous wall saturated with apotassium solution. The oxygen is transformed at the cathode intonegative hydroxyl ions which are discharged towards the anode. Thecurrent which passes between the two electrodes is thus proportional tothe quantity of oxygen present.

The CO₂ is measured by an apparatus of the COSMA Corporation which isbased on the principle of infra-red radiation absorption.

The results of the permeability measurements are set forth in Table 1.

                  TABLE 1                                                         ______________________________________                                                         PERMEABILITY, P 10.sup.10                                    PLATES ARE MADE  cm.sup.3 . mm/cm.sup.2 . sec . cmHg                          OF MIXTURES      of O.sub.2 of CO.sub.2                                       ______________________________________                                        No 1 kneaded into sheets                                                                       0.58       1.06                                              No 1 extruded into flasks                                                                      0.50       1.05                                              No 2 kneaded into sheets                                                                       0.38       0.70                                              No 2 extruded into flasks                                                                      0.06       0.07                                              No 3 kneaded into sheets                                                                       0.32       0.50                                              No 3 extruded into flasks                                                                      0.05       not measurable                                    ______________________________________                                    

The plates made out of the flasks having the lamellar structures,exhibit permeabilities significantly below those of plates made out ofsheets obtained from the cylinder mixer. In effect, for the sheetsobtained from the cylindrical mixer, the laminar flow condition is notfulfilled and there is thus no lamellar structure despite the relativelysignificant quantities of PVAL in mixtures 2 and 3. As a result, the O₂and CO₂ permeability is only slightly below that of mixture 1 whichcontains no PVAL.

EXAMPLE 2

A series of seven mixtures containing different volumetrical fractionsof PVAL (V') and PVC (V") as shown in table 2, is prepared. The mixturesfurther contain: 1 pcr of Paraloid® K 120 N, 0.3 pcr of solid thio-tinstabilizer and 0.3 pcr of Cire CP® lubricant.

The mixture of the components and the transformation of the mixturesinto 250 cc flasks by blower extrusion are effected by the devices andunder the conditions of example 1.

Table 2 sets forth the oxygen permeabilities, measured according to themethod described above. Table 3 sets forth the modulus of elasticity inflexion and traction the Vicat point under 5 kg for some of themixtures.

                  TABLE No 2                                                      ______________________________________                                         Mixture Number                                                                           V'     V"                                                                                   ##STR1##                                            ______________________________________                                        4          0.0    0.978  0.43          0.50                                   5          0.011  0.967  0.37          0.45                                   6          0.052  0.927  0.26          0.37                                   7          0.098  0.881  0.14          0.19                                   8          0.141  0.840  0.08          0.12                                   9          0.180  0.802  0.11          0.12                                   10         0.247  0.736  0.08          0.15                                   ______________________________________                                    

The slightly elevated values of PO₂ to the right of the columncorrespond to the flasks made by blower extrusion of recycled material.Materials rejected in the course of manufacturing can thus be reusedwhile preserving to a significant extent their increaaed O₂impermeability.

                  TABLE No 3                                                      ______________________________________                                                Units of MIXTURE No                                                   Characteristics                                                                         Measurement                                                                              4       7     9     10                                   ______________________________________                                        Modulus                                                                       of elasticity                                                                           Kgf/cm.sup.2                                                                             30 700  31900 33200 36 300                               (flexion) -Modulus                                                            of elasticity                                                                           "          26 600  --    28200 30 400                               (traction)                                                                    Vicat                                                                         point under                                                                             °C.  80       80    80   80                                  5 Kgf                                                                         ______________________________________                                    

The increase in the modulus of elasticity is of particular significancewhen packaging carbonated beverages in PVC bottles since it assures agreater dimensional stability. As a result, thinner bottle walls may beused which of course results in the use of less material and in lowercost.

The increase in O₂ impermeability is evidenced likewise by measurementsperformed directly on the 250 cc flasks made by blower extrusion. Themeasurement method used is that described by Calvano et al in ModernPackaging, Nov. 1968, pages 143-145. The average thickness of the wallsof the flasks was approximately 0.65 mm. Table 4 sets forth the O₂permeability coefficients (PO₂), determined by this method.

                  TABLE No 4                                                      ______________________________________                                         Mixture Number                                                                                   ##STR2##                                                  ______________________________________                                        4                  0.55                                                       8                  0.037                                                      9                  0.022                                                      10                 not measurable                                             ______________________________________                                    

The PO₂ coefficients of mixtures 8, 9 and 10 obtained by directmeasurement on the flasks are substantially less than those of Table 2which were measured on pressed plates having a thickness of 0.1 mm. Thedifference may possibly be due to the non-linearity of the coefficientsas a function of thickness as a result of the lamellar structure of thematerial. In effect, it is possible that as the number of lamellarinterfaces increases with increasing thickness, supplemental resistanceis produced on the passage of the molecules of gas. This may be due tothe progressive decrease in the pressure gradient across the lamellarmaterial.

Examples 1 and 2 show quite clearly that in the case of PVC the processof the invention makes it possible to improve the gas impermeability andmodulus of elasticity of the PVC. These properties are of course ofprimary significance when packaging materials which are oxygen sensitiveor which contain carbon dioxide gas in PVC containers capable ofmaintaining their structural integrity.

The specification, the drawing and the examples present a detaileddisclosure of the invention. It is to be understood however that theinvention is not limited to the specific methods, of manufacture, ofmethods of use, compositions and articles specifically disclosed butextends instead to all modifications and alternatives falling within thescope of the invention as it is defined by the claims.

I claim:
 1. A process of manufacturing a sheet-like thermoplasticstructure having a reduced permeability to gases comprising a continuousphase consisting essentially of polyvinyl chloride and a discontinuousphase consisting essentially of polyvinyl alcohol, incompatible with thepolyvinyl chloride phase, comprising lamellar layers distributed in thecontinuous polyvinyl chloride phase parallel to the surface of saidsheet-like structure, which comprises:(a) mixing polyvinyl chloride withpolyvinyl alcohol to provide a polymer mixture; (b) gelling said mixtureunder the combined effects of pressure and heat, and (c) extruding thegelled mixture by subjecting the gelled mixture to laminar flow throughat least one die, said die providing between a die inlet and a dieoutlet a flow path for said mixture, at least a portion of which flowpath is defined by the interval between two spaced parallel surfaces,the ratio of the length of said surfaces in the direction of flow to thedistance between said surfaces being greater than
 10. 2. The process ofclaim 1, wherein said ratio of the length of said parallel surfaces tothe distance therebetween is greater than
 20. 3. The process of claim 1or 2, wherein said die outlet has a rectangular configuration.
 4. Theprocess of claim 1 or 2, wherein said die outlet has an annularconfiguration.
 5. The process of claim 1 or 2, wherein said polymermixture is prepared by mixing 100 parts by weight of polyvinyl chloridewith about 5 to 30 parts by weight of polyvinyl alcohol.
 6. The processof claim 1 or 2, wherein the K value of the polyvinyl chloride iscomprised between about 50 and about 80, the extent of hydrolysis of thepolyvinyl alcohol being comprised between about 50% and about 100%, andthe viscosity of a 4% aqueous solution of the polyvinyl alcohol beingcomprised between about 2 cP and about 70 cP.
 7. The process of claim 5,wherein the K value of the polyvinyl chloride is comprised between about50 and about 80, the extend of hydrolysis of the polyvinyl alcohol beingcomprised between about 50% and about 100%, and the viscosity of a 4%aqueous solution of the polyvinyl alcohol being comprised between about2 cP and about 70 cP.
 8. The process of claim 1, further comprising thestep of incorporating in said polymer mixture at least one of thecompounds selected from the group consisting of stabilizers, lubricants,coloring agents and shock resisting agents.
 9. The process of claim 5,further comprising the step of incorporating in said polymer mixture atleast one composition selected from the group consisting of stabilizers,lubricants, coloring agents and shock resisting agents.
 10. The processof claim 6, further comprising the step of incorporating in said polymermixture at least one composition selected from the group consisting ofstabilizers, lubricants, coloring agents and shock resisting agents. 11.The process of claim 7, further comprising the step of incorporating insaid polymer mixture at least one composition selected from the groupconsisting of stabilizers, lubricants, coloring agents and shockresisting agents.